Review - Thermal comfort in ruminants and equines

Acknowledgements The authors thank Luc Mounier and Deborah Temple for reviewing this document. Review Thermal comfort in ruminants and equines Version 2 Maria-Anastasia Karatzia, Domenico Vecchio, Evangelia Sossidou and Isabelle Veissier (chair) REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines This review is a publication of the European Union Reference Centre for Animal Welfare for Ruminants & Equines. EURCAW Ruminants & Equines was designated by the European Commission through implementing decision of 6 May 2021, in accordance with Regulation 2017/625/EU. Disclaimer This review can be downloaded for free at https://doi.org/10.5281/zenodo.17661637 Citation: Karatzia, M.A., Vecchio, D., Sossidou, E. & Veissier, I. (2025). Review - Thermal comfort in ruminants and equines. EURCAW Ruminants & Equines. Each EURCAW Ruminants & Equines review provides background information on the biological relevance of the welfare topic. It then presents the most important key areas to focus on during welfare inspections, describes why welfare issues occur and lists specific animal-based indicators that can help official inspectors to identify these welfare issues. Finally, the review summarises good and better practices that can help to solve the previously described welfare issues, and deals with related legislative requirements. EURCAW Ruminants & Equines produces its reviews according to internationally accepted scientific standards, which include an external peer review process. However, it cannot accept liability for any damage resulting from the use of the results of this study or the application of the advice contained in it. [email protected] https://www.eurcaw-ruminants-equines.eu/ https://www.linkedin.com/company/eurcaw-ruminants-equines/ Review Thermal comfort in ruminants and equines Maria-Anastasia Karatzia1, Domenico Vecchio2, Evangelia Sossidou1, Isabelle Veissier3 (chair) 1Veterinary Research Institute, Ellinikos Georgikos Organismos-DIMITRA, ELGO-DIMITRA Campus, Thermi, Greece 2Italian National Reference Centre on Water Buffalo Farming and Productions Hygiene and Technologies (CReNBuf), Istituto Zooprofilattico Sperimentale del Mezzogiorno, Portici, Italy 3UMR Herbivores, University Clermont-Auvergne, INRAE, VetAgro-Sup, 63122 Saint-Genes-Champanelle, France November 2025 REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines Contents 1 Executive Summary ______________________________________________________ 5 2 Foreword _______________________________________________________________ 5 3 Definitions ______________________________________________________________ 7 4 Adaptation to thermal conditions ____________________________________________ 8 4.1 Adaptations to cold ___________________________________________________ 8 4.2 Adaptations to heat ___________________________________________________ 9 5 Conditions for thermal comfort according to animal types ________________________ 10 5.1 Concepts and indices _________________________________________________ 10 5.1.1 Thermoneutrality and thermoneutral zone _______________________________ 10 5.1.2 Thermal comfort zone ______________________________________________ 11 5.1.3 The temperature humidity index ______________________________________ 13 5.1.4 The heat load Index ________________________________________________ 13 5.1.5 Accumulated heat load ______________________________________________ 14 5.2 Thermal range per species _____________________________________________ 14 5.2.1 Cattle ___________________________________________________________ 14 5.2.2 Sheep ___________________________________________________________ 15 5.2.3 Goats ___________________________________________________________ 16 5.2.4 Buffalo __________________________________________________________ 16 5.2.5 Cervids __________________________________________________________ 16 5.2.6 Camelids ________________________________________________________ 16 5.2.7 Equids __________________________________________________________ 17 6 Thermal ranges in European countries _______________________________________ 17 7 How to ensure thermal comfort ____________________________________________ 18 7.1 Protection against heat _______________________________________________ 19 7.1.1 Limiting the production of heat by the animal ____________________________ 19 7.1.2 Reducing heat load from the environment _______________________________ 20 7.1.2.1 Limiting radiation ________________________________________________ 20 7.1.2.2 Accelerating convection ___________________________________________ 21 7.1.2.3 Facilitating evaporation and conduction _______________________________ 21 7.2 Protection against cold ________________________________________________ 22 7.2.1 Increasing the production of heat by the animal __________________________ 22 REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 7.2.2 Limiting heat losses ________________________________________________ 22 7.2.3 Providing extra heat ________________________________________________ 22 7.2.4 Special case: parturition and neonates _________________________________ 22 8 Key factors to focus on during welfare inspections ______________________________ 23 9 Gaps in knowledge and further studies needed ________________________________ 25 10 Conclusions ____________________________________________________________ 25 11 References ____________________________________________________________ 26 REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 5 1 Executive Summary Like all animals, farm animals are adapted to a certain range of thermal conditions, often defined by air temperature and humidity. Animal management systems and geographical location within the EU typically determine the risks of exposure to heat or cold stress. In the past, heat stress was experienced by animals mainly in southern Europe and cold stress was experienced by animals mostly in northern Europe. However, during the 21st century, the temperature will reach levels corresponding at least to moderate heat stress in most European regions (Carvajal et al., 2021; Hempel et al., 2019). Animals react to heat by decreasing feed intake, decreasing their basal metabolism (associated with reduced metabolic heat production), increasing their respiratory rate (possibly with panting), looking for shade and reducing their activity. Animals react to cold by increasing feed intake, increasing their basal metabolism (production of glucose, fatty acids in ruminants) to generate metabolic heat, staying close to other animals, avoiding cold areas and draughts, staying more often in sunlight or in areas protected by vegetation or a shelter. The thermoneutral zone (TNZ), that is the thermal zone in which an animal does not have to generate or lose heat to maintain its body temperature, depends on the species, the breed (e.g. dairy vs. beef breed), the age and the vigour of the animal. It ranges from -5 to 25 °C for dairy cows, 5 to 25 °C for horses, 6 to 27 °C for goats and 12 to 27 °C for ewes. Young animals are more sensitive to cold than adults. Animals can be protected from heat by providing shade in outdoor systems and adapting the ventilation during housing while ensuring that animals have access to cool or cold water, have limited physical exercise, and, specifically for ruminants, are fed either roughage of good quality or a more concentrated diet. Spraying water can also encourage evaporation that in turn cools animals. Animals can be protected from cold when housed by reducing draughts and air humidity, providing a deep litter, adequate feeding and warm water. Supplementary heating can also be used, especially for young animals. 2 Foreword European Union Reference Centres for Animal Welfare (EURCAWs) aim at improving the enforcement of the legislation on animal welfare, which is one of the Commission's priorities. The EURCAWs provide technical support and coordinated assistance to EU Member States in carrying out official controls in the field of animal welfare. The present review focuses on thermal comfort in ruminants and equids. Like all animals, farm animals are adapted to a certain range of thermal conditions, often described by air temperature possibly combined with humidity. Animal management systems and geographical location within the EU typically determine the risks of exposure to heat or cold stress. REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 6 In the past, heat stress was experienced by animals mainly in southern Europe and cold stress was experienced by animals mainly in northern Europe. However, according to climatic projections, the temperature will significantly increase in the 21st century (by 1–5 °C on average each year by the end of the century) and reach levels corresponding to at least moderate heat stress in most European regions and severe heat stress in some regions (Carvajal et al., 2021; Hempel et al., 2019). The EU legislation concerning the thermal range that farm animals must be kept in addresses only the issue of thermal stress. More specifically, EC Regulation 1/2005 for the transport of animals stipulates that it is necessary to “protect the animals from inclement weather, extreme temperatures and adverse changes in climatic conditions”. Again, according to Council Directive 98/58/EC that applies to all farm animals, housing conditions must avoid harm due to inappropriate thermal conditions. There is, however, a wide gap between harm due to extreme conditions and thermal comfort. The thermal conditions that animals can adapt to vary with factors such as species, age or adaptation capacities. However, the exact range of air temperature and humidity in which animals should be kept is not specified in Council Directive 98/58/EC, nor in Directive 2008/119/EC specific to calves. EC Regulation 1/2005 stipulates that ventilation systems must be capable of “maintaining a range of temperatures from 5 °C to 30 °C within the means of transport, for all animals, with a +/- 5 °C tolerance, depending on the outside temperature”, leading to a range of tolerated temperatures from 0 to 35 °C. Due to the increasing risks and the lack of clear recommendations, EURCAW Ruminants & Equines reviewed the knowledge available on thermal comfort in these species. In the present document, we first address how animals adapt to thermal conditions outside their thermoneutral zone, we then synthesise the information on thermal conditions that correspond to comfort and stress depending on species and age, we identify the risks in the EU, and we finally review solutions to ensure thermal comfort. REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 7 3 Definitions1 Accumulated heat load AHL An index that combines HLI and the time of exposure (Gaughan, Mader, Holt, & Lisle, 2008) Heat load index HLI An index that represents the combined effects of air temperature, humidity, wind speed, and radiation (Gaughan et al., 2008) Homeothermic animal An animal able to keep its body temperature at approximately the same level (i.e. within certain limits) despite changes in the ambient temperature. Lower critical temperature LCT The threshold of ambient temperature below which the rate of heat production of a resting homeothermic animal increases (e.g., by shivering) to maintain thermal balance Relative humidity RH The amount of water vapour present in air, expressed as a percentage of the amount required for saturation at the same temperature and pressure Temperature humidity index THI An index that represents the combined effects of air temperature and humidity (Hahn, Mader, & Eigenberg, 2003) Temperature, black globe T g The temperature of a black hollow sphere as measured by a thermometer at its centre. It represents the effects of ambient temperature, wind cooling and solar radiation (Li, Gebremedhin, Lee, & Collier, 2009) Temperature, dew-point T dp The temperature at which condensation first occurs when air is cooled at constant pressure. Temperature, dry bulb T db The temperature of gazes measured by a thermometer shielded from radiation Temperature, wet bulb T wb The lowest temperature to which a parcel of air can be cooled by evaporating water Thermal comfort zone TCZ The range of environmental temperatures included in TNZ, where specific mechanisms of thermoregulation are necessary to maintain core body temperature and the animal is in the preferred or chosen thermal environment (Silanikove, 2000) Thermogenesis The process of heat production in the body Thermoneutral zone TNZ The range of ambient temperatures within which the animal does not have to expend energy to maintain normal body temperature (Becker, Collier, & Stone, 2020) Thermoregulation The maintenance of temperature within certain limits despite variable internal or external heat loads Upper critical temperature UCT The ambient temperature above which the rate of evaporative heat loss of a resting thermoregulating animal must be increased (e.g., by thermal tachypnea or by thermal sweating) in order to maintain thermal balance. 1 Most definitions are from The Commission for Thermal Physiology of the International Union of Physiological Sciences (2001) except if otherwise stated REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 8 4 Adaptation to thermal conditions Ruminants and equids are classified as homeothermic animals as they can uphold a stable internal body temperature despite fluctuations in ambient conditions within a certain range. The physiological mechanism that regulates the balance between heat acquisition and dissipation through interactions with the environment to uphold a stable body temperature, is called thermoregulation (Al-Ramamneh, 2023; Santos, Souza-Junior, Dantas, & Costa, 2021). 4.1 Adaptations to cold Adaptation to cold refers to modifications/changes that occur to minimise the impact of low temperatures. The threshold below which a temperature corresponds to cold varies with several factors such as species or age (see Section 5 – Conditions for thermal comfort according to animal types). In cold conditions, animals adjust their behaviour towards heat retention: they can gather in groups, restrict standing time to limit exposure to wind, avoid resting on cold areas, and stay in direct exposure to solar radiation (sunbathing), or in areas protected by vegetation or shelter (Terrien, Perret, & Aujard, 2011). In cold conditions, thermogenesis, that is, generating heat from the body metabolism, is enhanced, namely glucose synthesis and glycolytic activity (Doubek, Slosárková, Fleischer, Malá, & Skrivánek, 2003). The metabolic changes are mediated by increased levels of cortisol (Leite, Façanha, Bermejo, Guilhermino, & Bermejo, 2021). Muscles and veins may contract, resulting in shivering and vasoconstriction that respectively produce heat and limit heat loss, and the heart rate increases (Lima et al., 2022). These responses are mediated by the sympathetic nervous system. In ruminants, increased feed intake also boosts the production of heat through ruminal digestion. Exposure to cold can make animals, especially young animals, more sensitive to health disorders. In cold conditions, young animals are more sensitive to respiratory and intestinal infections (diarrhoea), their growth can be impaired, and their mortality can increase (calves: Hyde, Green, Hudson, & Down, 2022; F. L. M. Silva & Bittar, 2019) (lambs: Guo et al., 2021; Masters et al., 2023). For instance, calves exposed to cold stress are at a greater risk of developing bovine respiratory disease (BRD) (Roland, Drillich, Klein-Jöbstl, & Iwersen, 2016). When environmental conditions become too cold for the adaptive mechanisms of an animal to be able to remain within the thermoneutral zone (TNZ), body core temperature, heart rate and respiratory rate drop; in extreme cases this can lead to death. In ruminants facing long-term cold conditions the production of volatile fatty acids (VFA) in the rumen decreases significantly, resulting in a decrease in apparent feed digestibility (Rashamol et al., 2018). Continuous exposure of an animal population (a species or a breed) to cold conditions can result in the selection of animals that are genetically more adapted to such conditions (Berihulay, Abied, He, Jiang, & Ma, 2019). Morphological adaptations to cold stress include the development of compact-framed bodies that provide a reduced skin surface, and thick fleece that covers a REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 9 significant extent of the body and its layers repel moisture and augment heat preservation (F. L. M. Silva & Bittar, 2019; Wang, Li, Peng, & Niu, 2023). 4.2 Adaptations to heat Adaptation to heat refers to modifications/changes that occur to minimise the impact of high temperatures. The threshold above which a temperature corresponds to heat varies with several factors such as species or age (see Section 5– Conditions for thermal comfort according to animal types). In hot conditions, animals usually drink more, reduce their activity (they are unwilling to move and decrease feed intake), stay standing rather than lying, and seek shade, while respiration rate increases and panting may occur, i.e. the animal takes short and quick breaths (Kumar, Singh, Sahoo, & Naqvi, 2014; Ratnakaran et al., 2016). Reduced activity limits thermogenesis, while shade protects against solar radiation and panting increases evaporation (see below section 7.1 Protection against heat). In hot conditions, the basal metabolism is reduced, mediated by alteration of hormonal secretion such as a reduction in thyroid and growth hormone production (Salama et al., 2014). As feed intake is reduced, energy balance drops. It results in reduced performance in terms of milk yield, reproductive efficiency and growth, in high-producing animals in particular (Lima et al., 2022). At the same time, cortisol is released, probably due to psychological stress (Salama et al., 2014). Converting water from the body into vapour helps to reduce heat load (evaporative thermolysis). Respiratory frequency thus increases in hot conditions, possibly combined with panting, openmouth breathing and hypersalivation, and sweating (Mascarenhas et al., 2023; Olsson, 2005) When panting, the inhaled air cools the veins passing around arteries at the base of the brain and so, brain temperature remains lower than the rectal temperature. Panting is generally considered to be less effective than sweating in ruminants (Olsson, 2005; Silanikove, 2000). Sweating ceases at the onset of dehydration, but can still cause electrolyte imbalance (Olsson, 2005). Sweating is more marked in equids – especially horses – than ruminants. In Zebu cattle sweat glands are larger, thus sweating is more effective than in temperate cattle breeds (Hansen, 2004). An added stressor which animals under hot conditions have to cope with, is water scarcity. Indeed, hot environmental conditions favour the evaporation of shallow ground water reserves, which are often the main source of water for grazing ruminants. Water deprivation can elicit complex, nonspecific responses that are detrimental to animal’s health and productivity and is even connected to increased morbidity and mortality (El Mahdy, Boaru, Popescu, & Borda, 2016; Veerasamy Sejian et al., 2021). Small ruminants in semi-extensive and extensive systems are more likely exposed to such a deprivation than other ruminants or equines. Despite their small body size and a lower absolute requirement for water in comparison to cattle, small ruminants suffer when clean and cool water is not provided regularly. If they do not drink enough water, heat dissipation fails and milk secretion cannot be maintained (Veerasamy Sejian et al., 2021). When water becomes scarce, its quality and safety can also deteriorate with increased salinity, and increased concentration of minerals, manure, microorganisms, chemicals or algae contamination. Salinity, REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 16 Similarly, the LCT of shorn sheep is only 10 °C whereas the LCT of fully fleeced wool sheep reaches 0 °C (EFSA Panel on Animal Health and Welfare et al., 2021). For lambs, TNZ seems to range between 14 and 21 °C (EFSA Panel on Animal Health and Welfare et al., 2021). 5.2.3 Goats Information on optimal thermal conditions for goats is scarce. TNZ seems to be between 6 °C and 27 °C (TCZ, between 10 and 18 °C), with relative humidity ranging from 60 to 80% and wind speed of 0.5 m/s (Toussaint, 1997). 5.2.4 Buffalo For buffaloes, TCZ is between 13 and 18°C in combination with relative humidity around 55–65% and wind velocity of 5–8 km/h. As TNZ is concerned, LCT is not defined and UCT is set at 25°C (Payne & Williamson, 1990). High environmental temperature coupled with high humidity is highly detrimental to buffaloes’ growth, reproduction, and production (Marai & Haeeb, 2010). THI (calculated according to Formula 2) below 72, between 72 and 80, between 80 and 85 and beyond 85 correspond to no stress, mild stress, severe stress and lethal stress (Akyuz, Boyaci, & Cayli, 2010; Kohli, Atheya, & Thapliyal, 2014). 5.2.5 Cervids Cervids are well adapted to cold, with LCT at – 28 °C for adult reindeer and – 23 °C for their calves. By contrast, they are not well adapted to heat, with UCT of + 15 °C in adult reindeer and + 20 °C in their calves (Soppela, Nieminen, & Timisjàrvi, 1986). In red deer, adult females suffer from heat at THI above 60 (e.g. air temperature 16 °C; relative humidity 60 %) and calf growth is impaired when THI is above 72 (e.g. air temperature 25 °C; relative humidity 60 %) (PérezBarbería et al., 2020). 5.2.6 Camelids For dromedary camels, TNZ seems to be between 10 and 40 °C in dry conditions (Samara & Alhaidary, 2014). However, differences may exist between breeds, age, hydration status, body condition, and sex (Alhaidary et al., 2013). Finally, it should be considered that these temperatures and those of TNZ indicated by Samara and Al-Haidary were obtained at low relative humidity values (Samara & Alhaidary, 2014). A THI calculated (according to Formula 1) below 71 (e.g. 24 °C with 50 % of relative humidity) corresponds to no stress. At THI above 71, the core body temperature and the skin temperature increase exponentially (Habte et al., 2021). A core body temperature increasing up to 38 °C at 3 PM in the dry season suggests that camels at THI 77 (31 °C with 34 % of relative humidity) fall outside the TCZ, probably approaching UCT. However, even during the hot and dry season camels did not show significant decreases in milk production, suggesting that they do not experience severe heat stress at 38 °C (Habte et al., 2021). However, a THI of 81 or more (40 °C with 6.9 % of relative humidity) leads to a change in blood metabolites and haematological indices, REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 17 suggesting that the camels experience severe heat stress (Abdoun, Samara, Okab, & Al-Haidary, 2012). 5.2.7 Equids For horses, TNZ ranges from 5 °C to 25 °C (Morgan, 1998). According to the commencement of evaporative heat loss and sweating, the upper threshold of TCZ is around 20 °C (EFSA Panel on Animal Health and Welfare et al., 2022). The Federation Equestre Internationale uses WBGT to take into account thermal comfort during competitions. A WBGT above 28 °C requires precautions to reduce thermal stress, e.g. by using misting fans, and WBGT above 33 °C is not compatible with competition (Jeffcott, 1996; D. Marlin & Williams, 2018; D. J. Marlin, Misheff, & Whitehead, 2018; Schroter, Marlin, & Jeffcott, 1996). 6 Thermal ranges in European countries Since the 1980s, climatic temperatures have shown long-term warming trends. Europe is the fastest warming continent; since the 1980s, warming in the continent has been about double the global rate (European Environment Agency, 2024). The global average annual temperature in 2023 exceeded pre-industrial levels by 1.5 °C, it also exceeded levels between 1991–2020 average across most of Europe, with a 1.02–1.12 °C increase on average (Copernicus Climate Change Service (C3S), 2024). The largest anomalies were in eastern and central Europe, with up to 2.6 °C increase in parts of eastern Europe and 2.3 °C in parts of the Alps (compared to 19912020). By contrast, in Scandinavia and Iceland, temperatures dropped by 1 °C below average in 2023. Europe also faces increasingly severe climate risks, including prolonged heatwaves and droughts, heavy rainfall causing pluvial and riverine flooding, and rising sea levels causing coastal flooding (Copernicus Climate Change Service (C3S), 2024). The climate risks differ between European regions (Table 1). Across Europe, there is an increasing number of hot days and a decreasing number of cold days. In 2022 a record number of very severe heat stress days occurred (temperatures between 38 and 46 °C), 2023 saw a record number of extreme heat stress days (temperatures above 46 °C) (Copernicus Climate Change Service (C3S), 2024), where the distinction between severe, very severe and extreme heat stress is related to human thermal comfort (according to the Universal Thermal Climate Index (UTCI), Bröde et al., 2012). In 2023, all of Europe, apart from the Nordic region and Ireland, experienced at least a few days of severe heat stress (temperatures between 32 and 38 °C), with up to 60–80 days of severe heat stress in parts of southern Europe. Much of southern Europe also experienced several days of very severe heat stress, with up to 80 days recorded in southern Spain. Parts of southern and eastern Spain, south-western France, southeastern Italy, southern Sardinia, Greece and western Turkey experienced up to 10 days of extreme heat stress (Copernicus Climate Change Service (C3S), 2024). REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 18 Heatwaves correspond to exceptional circumstances. There is no internationally agreed definition of a heatwave. According to the European State of the Climate 2023 (Copernicus Climate Change Service (C3S), 2024), a heatwave is a period of at least three days with the daily air temperature minima and maxima exceeding the highest 5 % of values for that day during 1991–2020. According to the European Climate Adaptation Platform (Climate-ADAPT), a heatwave is a period of at least three days with the daily air temperature maxima exceeding the 99th percentile of the May to September season during a reference period. Heatwaves are getting more frequent in Europe (Baldi, Dalu, Maracchi, Pasqui, & Cesarone, 2006; Zampieri et al., 2016). The Mediterranean area is a climate change hot spot as it stands out as one of the most critical areas for heatwaves (Efthymiadis, Goodess, & Jones, 2011; Giorgi, 2006; Giorgi & Lionello, 2008; Ulbrich et al., 2012). This specific climate signal has become more evident in the second half of the 20th century and this trend is very likely to continue. Table 1: Trends in climatic risks in Europe according to region (adapted from European Environment Agency EEA, report 01/2024; The low scenario corresponds to SSP1-2 and the high scenario to SSP3-7 from the 6th GIEC report. Region North1 West2 Center-East3 South4 Scenario Low High Low High Low High Low High Mean temperature + + + + + + + + Heatwave days5 + + + + + + + + Total precipitation (+) + ? (-) (+) ? (-) - Heavy precipitation (+) + (+) + (+) + (+) + Drought (-) - ? + ? + + + 1Ireland, Norway, Sweden, Finland, Denmark, Estonia, Latvia, Lithuania 2France, Belgium, Netherlands, Germany, Switzerland, Austria 3Poland, Czech Republic, Slovakia, Hungary, Romania, Bulgaria 4Portugal, Spain, Italy, Slovenia, Croatia, Bosnia, Montenegro, Kosovo, Serbia, Macedonia, Greece, Turkey 5Days with a maximum temperature > 35 °C +, increase; -, decrease; (), limited agreement between models; ?, low confidence in direction of change 7 How to ensure thermal comfort When the ambient environmental conditions and the animal differ in their temperature, thermal energy is exchanged between them in the form of sensible energy exchanges, by thermal radiation, convection or conduction, or latent energy exchanges (Hoff, 2013). Thermal radiation corresponds to heat transfer by electromagnetic waves; either from the sun or surfaces of the environment not necessarily in contact with the animal. Conduction results from physical contact (direct molecular collision) with the environment. Convection corresponds to internal movements of a fluid (air, water, …), involving the transport of the properties of the fluid's particles as it moves. The difference in temperature between an animal and a surrounding fluid can induce convection which in turn increases exchanges by conduction between an animal and its environment. This process is sometimes mistakenly referred to as convection. Latent exchanges REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 19 result from liquid-to-vapour changes called evaporation, a process that consumes energy. Maintaining the animal within its TNZ can be achieved through animal management (to increase or reduce its production of heat) or acting on the environment to optimise radiation, conduction, convection or evaporation (Figure 2). Figure 2: Heat exchanges between the animal and the environment. Note that conduction happens not only via contact with the ground but also via the contact of any part of the body and the surrounding and can be increased by convection (especially of the air). 7.1 Protection against heat 7.1.1 Limiting the production of heat by the animal Feeding contributes largely to the production of metabolic heat by the animal. Mitigation strategies include moving feed distribution to the coolest periods of the day (end of afternoon and night) and by reducing the amount of carbohydrates, especially forage (reviewed by Brown-Brandl, 2013). In ruminants, more concentrates and more lipids can be incorporated to the diet (Yasothai, 2014). Access to water is essential during hot ambiant conditions. Drinking cool water helps to dissipate body heat (reviewed by Brown-Brandl, 2013). Having access to water at 24–28 °C rather than 38–44 °C helps sheep maintain their feed intake and body weight in case of hot weather (De et al., 2020). Also, the need for water is increased due to evaporation of water from the skin (see below). Dairy cows drink more in the case of hot weather, e.g. 1.2 L more per 1 °C increase (Murphy, Davis, & McCoy, 1983). REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 20 The presence of other animals increases the exchange of heat. Therefore, high stocking density and overcrowding increase the risk of heat stress during high ambient temperatures. Animals should have a large space allowance when they are housed indoors or shade when outdoors. Sheep nevertheless often gather in the same place (usually shaded or with some air draught) in the case of heat, they lower their head presumably to benefit from the shade made by other animals. Muscle activity also produces heat. Typically, body temperature rises during physical exercise and may require a few hours to return to initial levels; e.g. body temperature can increase from 38 °C to nearly 41 °C in cattle handled and restrained in a squeeze chute (T.M. Brown-Brandl, 2013). It is thus recommended not to handle, move or transport animals during high ambient temperatures. Similarly, working animals should also not work during such conditions (Sossidou, Termatzidou, Marinou, Cerasoli, & Collins, 2024). Modifying milking times for dairy animals should also be considered, e.g. milking early in the morning and late at night to avoid moving animals during hot times of the day. In hot conditions, ruminants kept outdoors on extensively managed pastures should receive special attention. In hot conditions, pasture forage may be scarce and of low quality (fibrous) which increases the production of metabolic heat. Animals will then suffer from both heat and undernutrition. In addition, they may have to walk more to find their food or to find water, increasing heat load due to physical exercise. In hot conditions, animals kept outdoors at pasture may thus need to be supplemented with protein and fat to adequately meet their nutritional needs while limiting heat production (Silanikove 2000), access to water needs to be facilitated (to prevent animals from walking long distances), and shade must be available (see below). 7.1.2 Reducing heat load from the environment 7.1.2.1 Limiting radiation Shade reduces exposure to solar radiation. In the case of hot weather, animals look for shade and this lowers their body temperature (Edwards-Callaway et al., 2020; Veissier et al., 2018). Shade can be provided outdoors with trees or artificial shelters, or a combination of both, e.g. cloth stretched between trees (Veissier et al., 2018). When shade is provided with a shelter, it is essential that the roof of the shelter is high enough or insulated to reduce radiation from the roof and allow air circulation, and the shelter should be oriented so as to benefit from prevailing wind (Nienaber & LeRoy Hahn, 2004; Shoshani & Hetzroni, 2013). Cool roof designs have primarily been developed for humans to optimise the reflection of solar radiation. They are typically covered with white materials. Such cool roofs are efficient at reducing the temperature inside barns (by at least 3 °C) and the impact of hot weather on animals (e.g. limiting the reduction in milk production) (Santunione, Libbra, & Muscio, 2017). Solar panels are becoming popular as a means to provide shade at pasture. Indeed, solar panels can reduce 30–40 % heat load from solar radiation at its peak during the day. Sheep and cattle REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 21 seek shade under solar panels during high solar radiation, which lowers the increase in body surface temperature (Carvalho Fonsêca et al., 2023; Faria et al., 2023). In case of very hot weather, animals may be moved indoors during the day to avoid the hottest hours, and they may graze at night (Fournel, Ouellet, & Charbonneau, 2017). In the northern hemisphere, pastures or outdoor paddocks exposed south, west, or south-west receive the most solar radiation. To mitigate against heat stress, animals can be kept at pastures with lower exposure to solar radiation (reviewed by T.M. Brown-Brandl, 2013). Similarly, in summer, air temperature in hutches can be above the TNZ for calves; it is therefore recommended to place them facing north or east (Bakony, Jurkovich, Kiss, & Kovács, 2021). 7.1.2.2 Accelerating convection Heat losses by convection can be increased indoors using fans or optimising barn ventilation on the condition that the air is cooler than the animal. Barns for ruminants typically use natural ventilation, with air entering the barn from low openings on the building sides and going out of the building through openings on the building ridge (Hoff, 2013). 7.1.2.3 Facilitating evaporation and conduction The principle of evaporation can be used to cool the air that enters a barn. This can be obtained with fans equipped with sprinklers (Bleizgys, Naujokienė, & Čėsna, 2022). Evaporation is more often targeted at the animals, i.e. water from the skin surface evaporating thus allowing animals to decrease their body temperature. Evaporation from animals can be increased using sprinklers and increasing air speed with fans (D'Emilio, Porto, Cascone, Bella, & Gulino, 2017; Pérez-Barbería et al., 2021; Vitali, Grossi, & Lacetera, 2024). To be more effective, the water must enter the hair coat rather than staying at its surface. Therefore, misters are considered less effective to increase evaporation than sprinklers (Mitloehner et al., 2001, cited by T.M. Brown-Brandl, 2013). Spraying water with sprinklers abates body temperature by evaporation and conduction (Tresoldi, Schütz, & Tucker, 2018). Wallowing and bathing are natural behaviours of water buffaloes to combat hot weather (Napolitano, Pacelli, Grasso, Braghieri, & De Rosa, 2013). In farm conditions, buffaloes may not have access to water and mud to perform such behaviours and should be sprayed with cool water in case of hot weather (Bah, Shahid, Pasha, & Javed, 2022). A pool with cool water has nevertheless been used with success to reduce heat stress in Alpacas in a zoo in a hot region whereas Alpacas are native to cold regions and suffer from heat (Peng, Fu, Lee, & Tsai, 2019). Water is more conductive than organic material like straw. The litter or the ground must be kept clean from manure and drained to reduce heat load (reviewed by Brown-Brandl, 2013). When misters and sprinklers are used, proper drainage of the facilities must be ensured to avoid stagnant water. REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 22 7.2 Protection against cold In cold conditions, one can act by increasing heat production by animals, limiting heat losses (by convection, conduction, or evaporation), and providing extra heat. 7.2.1 Increasing the production of heat by the animal In ruminants, the digestion of roughage increases metabolic heat production. Therefore, their diet should contain a large proportion of roughage in cold weather. At the same time the animals need more energy to maintain their body temperature. It is thus essential that roughage of good quality is offered and in large amounts. In ruminants, drinking very cold water can affect ruminal fermentation (by decreasing the ruminal temperature). Animals tend to drink less during cold weather. Thus, ruminants and equines should be provided warm water (e.g. 31 °C, Petersen, Muscha, Mulliniks, & Roberts, 2016) in cold conditions. In some cold regions, heated drinkers are used, which avoid freezing of the water and optimise water intake. Finally, maintaining animals in groups rather than alone allows them to benefit from the heat of others; this is particularly true for young animals that stay with their dam. 7.2.2 Limiting heat losses The impact of cold ambient temperatures is increased by exposure to wind and precipitation. Indoor housing protects the animals against wind, rain and snow. Alternatively, animals, except young ones, can stay outdoors in case of cold weather in European conditions, provided they have access to shelter (Van Laer, Moons, Sonck, & Tuyttens, 2014). The shelter should be oriented to protect animals against dominant winds. Animals can also use natural shelter from trees and bushes (Van Laer et al., 2015). Vulnerable animals, including young animals, may require extra protection with jackets. Deep bedding buffers the animals from a cold floor or ground, limiting heat loss by conduction. 7.2.3 Providing extra heat In most EU countries, ruminants and equines do not need other measures than those mentioned above to resist cold. This, however, is not true for young animals (e.g. calves, lambs, kids). Radiant heat lamps are often used for these animals (Hoff, 2013), which transfer heat to animals by radiation. 7.2.4 Special case: parturition and neonates Neonates are very sensitive to thermal conditions, especially cold. In case of cold conditions (below TNZ), it is essential that neonates are kept in a well-bedded shelter that provides protection from wind / air draughts and that they are fed increased amounts of colostrum or milk (reviewed by Silva et al., 2021). The bedding, e.g. straw, should be dry and deep enough to allow neonates to nestle into it. The energy requirements of neonates are higher during cold ambient temperature; for instance, at -10°C, the energy requirement for body maintenance of a calf is twice that at 20 °C (Drackley, 2008). Colostrum is very nutritive and helps the neonate to cope with cold (Fernanda Lavinia Moura Silva et al., 2021). An additional provision of colostrum is necessary when the REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 23 ambient temperature drops below LCT. In addition, as mentioned above, radiant lamps can help young animals keep warm. Neonates born from a dystocial parturition and twin neonates are especially sensitive to cold because of a low heat production resulting from a low mobilisation of body lipids due to low plasma thyroid hormone levels (Masters et al., 2023; Vermorel, Dardillat, Vernet, Davicco, & Demigne, 1983). They should thus receive extra care in cold conditions. In case parturition is likely to take place during cold weather, it is important that females receive increased amounts of food during the last third of gestation to ensure adequate production of colostrum to protect the neonate. When approaching parturition, females should be able to isolate from the rest of the herd, e.g. they can be placed in a parturition pen with a clean, dry and deep bedding and with protection against draughts. The neonate must be carefully monitored: if the dam does not lick the neonate, it must be dried, and the intake of colostrum must be checked. As a last resort, e.g. if the calf is weak, colostrum may be provided via an oesophageal tube (See thematic factsheet ‘Colostrum provision to calves’). 8 Key factors to focus on during welfare inspections Animal-based measures, such as behaviour (e.g. changes in lying vs. standing time, animals gathering, searching for sun vs. shade), respiration, and body temperature, can be used to assess if animals suffer from cold or heat stress. One can also consider ambient parameters (temperature, humidity, air speed and radiation). However, it is unlikely that an inspector will be present on the days when thermal stress occurs. Therefore, it is important to assess the risk for thermal stress according to the season, the region and activity (e.g. production system). There is more risk for an animal to suffer from cold stress in Nordic or mountainous regions, especially in winter, and from heat stress in Mediterranean regions, especially in summer. Depending on the most prevalent risks (cold vs. heat stress), mitigation strategies (e.g. shelter, ventilation, modification of the diet) must be considered (Tables 2 & 3). REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 24 Table 2: Indicators of cold and heat stress Area Indicators of risks of cold stress Indicators of risks of heat stress Animal1 Decreased body core temperature Increased body core temperature Goose bumps, piloerection Increased skin temperature Shivering Sweating Vasoconstriction Panting Increased heart rate Increased respiratory rate Reduced feed intake Reduced milk production Decreased fertility Increased glycemia2 Increased cortisol2 Increased time spent lying Increased time spent standing Ambient conditions Temperature below LCT Temperature above UCT Humidity Humidity Air speed (negative impact) Air speed (positive impact) Solar radiation Risks (depending on region & season) Estimated frequency of cold days Estimated frequency of heat days 1Animal’s reactions to cold vs. heat vary with species 2Not applicable during on-farm inspection Table 3: Indicators of mitigation strategies Mitigation strategies against cold Mitigation strategies against heat Protections in place Large amounts of good quality roughage in diet Low-fibre diet Feeding during coolest hours Warm drinking water Cool drinking water Animals in groups Large space allowance / animal Protection against wind, shelter Increase in convection and evaporation: Ventilation and fans possibly combined with sprinklers in barns; pool with cool water for buffaloes Protection against radiation: shade; cool roofs; hutches, paddocks, pastures exposed north to east Deep bedding Dry litter or ground For young animals: radiant lamps, jackets Avoidance of physical exercise (handling, moving, transport, work) REV-Ruminants-Equines-2024-01-EN Version 2 – November 2025 Thermal comfort in ruminants and equines 25 9 Gaps in knowledge and further studies needed The following gaps in knowledge were identified: • Lack of information for some species or animal types: - young animals (e.g. lambs, goat kids) - heifers. They may adapt to cold more than calves but do not generate as much heat as lactating cows and thus may adapt less to cold stress but more easily to heat stress than cows. - cervids - donkeys and equine hybrids • Lack of information on LCT (specially depending on animal age) • Need to move from THI to more sophisticated indices e.g. to include radiation, air speed (e.g. HLI) • Need to consider the accumulated effect of heat (e.g. using AHL) • Need to clarify the concept of thermal comfort zones/degrees of thermal stress and validate animal-based measures: these zones depend not only on environmental conditions but also on the potential of adaptation of animals (according to species, age and production phase). 10 Conclusions Thermal comfort is becoming a pressing issue in most European countries due to climate change that has increased average temperatures and the frequency and duration of heat waves. In general, farmed ruminants and equines show signs of thermal discomfort in the case of heat (polypnea, panting, release of stress hormones, behavioural changes (e.g. changes in lying and standing time), reduction in feed intake and in dairy animals, reduction in milk production). Heat stress should be mitigated by providing shade and shelter outdoors and ventilation in housing. Water sprinklers should also be considered for species and in regions most prone to heat waves. Additionally, access to cool or cold water, and limiting handling and physical exercise, as well as adapting diet and feeding management are key mitigation strategies for heat stress. By contrast, in winter, animals may be subjected to cold stress, especially when temperatures fall below 0 °C. Draughts and humidity should be avoided to limit the effects of cold while deep bedding helps animals to maintain their body temperature. Young animals are more sensitive to cold and can require supplementary heating. 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It focuses on ruminant and equine welfare and legislation, and covers the entire life cycle from birth to the end of life. EURCAW Ruminants & Equines’ main objective is a harmonised compliance with EU legislation regarding welfare in EU Member States. This includes: • Directive 98/58/EC concerning the protection of animals kept on farms; • Regulations 1/2005/EC and 1099/2009/EC concerning their protection during transport and slaughter; • Directive 2010/63/EU concerning the protection of animals used for scientific purposes; • Directive 2008/119/EC laying down minimum standards for the protection of calves. EURCAW Ruminants & Equines supports: • Inspectors of Competent Authorities (CAs); • Ruminant and equine welfare policy workers; • Bodies supporting CAs with scientific expertise, training, and communication. Website and contact EURCAW Ruminants & Equines’ website offers relevant and actual information to support enforcement of ruminant and equine welfare legislation. We offer a ‘Questions to EURCAW’ service for official inspectors, policy workers, and other personnel providing advice or support for official controls of ruminant and equine welfare in the EU. For more information go to https://www.eurcawruminants-equines.eu/questions-to-eurcaw/. Activities of EURCAW Ruminants & Equines • Coordinated Assistance Providing support, networking and Questions to EURCAW; • Welfare indicators, Assessment & Best Practice Identifying animal welfare indicators, including animal based, management based and resource-based indicators, that can be used to verify compliance with the EU legislation; • Scientific and technical studies Preparing Scientific Reviews of knowledge on welfare topics and identify research needs; • Training Developing training materials and training standards for official inspectors; • Communication and Dissemination Increasing awareness of our outputs via the website, twitter, and newsletter; Partners EURCAW Ruminants & Equines receives funding from DG SANTE of the European Commission and represents a collaboration between the following six partner institutions: • Swedish University of Agricultural Sciences, Sweden • Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise “G. Caporale”, Italy • French National Institute for Agriculture, Food, and Environment, France • University of Natural Resources and Life Sciences, Vienna, Austria • University College Dublin, Ireland • Ellinikos Georgikos OrganismosDimitra/Veterinary Research Institute, Greece